In the manufacture of steel pipe from sheet and plate according to the U-O method and the like wherein the cylindrical shaped sections after leaving the O-Press with the edges in an abutting relation to each other, it is necessary to join the pipe by a longitudinal seam weld. The welding operation is one of the most critical in the pipe making process therefore it is necessary to obtain sound and properly positioned welds. One of the problems encountered in welding the abutting edges of the O-shaped pipe is the inability to obtain pipe lengths wherein the edges of the sections to be welded are straight and entirely even. The longitudinal edges of a metal sheet or plate are sheared or milled to a width exactly suitable for the diameter of a cylindrical section to be formed in an O-Press or other forming means. After the sheet or plate is formed into a cylindrical shape, the abutting edges which form the weld seam may not be straight relative to the axis of the pipe. These edges may be curved, S-shaped or slightly spiral relative to the longitudinal axis of the pipe. Also, the formed cylinder may be bowed throughout its length thus causing additional misalignment of the weld seam with the theoretical longitudinal axis of the pipe. These conditions are often caused when physical stresses are changed or relieved during shearing and milling of the edges and in cold working of the plate during the forming process from the flat section to a cylindrical shape. In the typical longitudinal seam welding operation the formed pipe is first tack-welded at predetermined intervals or continuously along the full length of the pipe seam to hold the edges in close relationship while the finished inside weld is carried out. This may be done by an automatic tack-welding machine or may be done manually. In any event, the shaped pipe is clamped in the closed position so that the edges of the section are abutting when the tack-welding operation is carried out.
The pipe is then conveyed to the inside welders wherein a long boom or other traveling welding apparatus may be acurately positioned so that the welding head moves along the inside seam while depositing a weld which is designed to penetrate about 60% of the thickness of the plate or sheet as the case may be. The welding head is guided by a V-shaped wheel riding in a groove formed by the edges which must be bevelled to provide a weld groove during the edge forming operation for the pipe section. It is important that the weld penetrate to a sufficient depth within the plate to assure interlocking of the inside and outside welds and at least to an extent equal to about twenty percent (20%) of the interlocked weld.
In many operations the tack-welding is conducted according to the metallic inert gas welding process, that is, MIG process, and in most inside and outside seam welding operations, the conventional automatic submerged arc welding process is utilized. This particular invention as described hereinbelow is concerned with the proper alignment of the outside weld with the inside weld so that the critical interlocking of the weld nuggets is achieved.